Edward KissinAffiliation:
School of Communications Technology and Mathematical Sciences, University of North London, Holloway, London N7 8DB, Great Britain
Email:
e.kissin@unl.ac.uk

Victor S. ShulmanAffiliation:
School of Communications Technology and Mathematical Sciences, University of North London, Holloway, London N7 8DB, Great Britain – and – Department of Mathematics, Vologda State Technical University, Vologda, Russia
Email:
shulman_v@yahoo.com